1. Field of the Invention
The present invention relates to a turbine vanes having a cooling structure in a gas turbine and to a gas turbine.
2. Description of Related Art
In general, turbine blades and turbine vanes in gas turbines usually include cooling structures therein because they are used in high-temperature environments.
A known example for cooling turbine vanes is a configuration in which two or three cavities through which cooling air passes are provided and inserts (insert cylinders) are disposed in these cavities (see U.S. Pat. No. 4,312,624, Japanese Unexamined Patent Application, Publication No. 2002-161705, Japanese Unexamined Patent Application, Publication No. 2003-286805, and Japanese Unexamined Patent Application, Publication No. Hei-09-112205, for example).
In the case of the above-described configuration, one space (cavity) is basically formed between each of the inserts and the inner wall of each of the cavities. To control pressures in respective areas inside the cavity at different values, a method in which sealing dams or the like for partitioning this cavity are provided is known.
Cooling air for the turbine vane is supplied to the insides of the inserts at the same pressure as in a casing. The cooling air is blown out through a number of small holes formed in the inserts toward the inner walls of the above-described cavities and is used for cooling the turbine vane (impingement cooling).
The cooling air used for the impingement cooling blows out from the cavities to the outside of the turbine vane through through-holes connecting the cavities to the outside of the turbine vane. The blown-out cooling air covers the outer surface of the turbine vane like a film, thereby reducing the inflow of heat from high-temperature gas to the turbine vane (film cooling).
In order to properly carry out the above-described film cooling, it is necessary to reduce the pressure difference between the insides of the cavities and the outside of the turbine vane as much as possible.
FIG. 7 is a vane transverse sectional view of a conventional turbine vane 60.
In an airfoil part 61 forming a body 71 of the turbine vane 60, a plurality of cooling chambers C1, C2, and C3 are disposed from a leading edge LE to a trailing edge TE, and inserts 81 are arranged in the respective cooling chambers. Cooling air supplied to the airfoil part 61 is supplied to the inserts 81, blows out through impingement holes 84 provided in the inserts 81 to cavity spaces (spaces surrounded by inner walls 71a of the body 71 and the inserts 81), and is used to cool the inner walls 71a of the body 71. Then, the cooling air is discharged through film holes 73 provided in the airfoil part 61 into combustion gas, and is used to film-cool an outer wall 71b of the body 71 of the airfoil part 61.
However, as shown in FIG. 7, the outer surface of the airfoil part 61 of the turbine vane 60 along which combustion gas flows generally has a low combustion-gas pressure at a suction surface SS side where the blade is curved in a convex shape and has a high combustion-gas pressure at a pressure surface PS side where it is curved in a concave shape. Therefore, in order to maintain an appropriate pressure difference (film pressure difference) between the film holes at both sides, the pressures in the cavity spaces, which are communicated to combustion gas through the film holes 73, are high at the pressure surface PS side and are low at the suction surface SS side.
Specifically, the velocity of cooling air blowing out through the impingement holes 84 in the inserts 81 to the cavity spaces is low at the pressure surface PS side and is high at the suction surface SS side. Therefore, it is likely to excessively cool the suction surface SS side of the body, compared with the pressure surface PS side thereof.
To suppress this phenomenon, protrusion-like sealing dams 72 extending in a vane-longitudinal-section direction are provided on the inner walls 71a of the body 71 at the leading edge LE side and at the trailing edge TE side, so as to partition the cavity spaces into pressure-surface-side cavity spaces CP and suction-surface-side cavity spaces CS. In each of the cooling chambers, the sealing dams 72 are disposed at at least two positions (on the inner wall 71a or a partition wall P, close to the leading edge LE and the trailing edge TE).
The sealing dams 72 are designed to support the insert 81 from the inner wall 71a side of the body 71 and are also designed to separate the cavity space into the pressure-surface-side cavity space CP and the suction-surface-side cavity space CS to prevent the pressure-surface-side cavity space CP from communicating with the suction-surface-side cavity space CS, thus making the pressures in the cavity spaces different between the pressure surface PS side and the suction surface SS side.
These sealing dams 72 are protrusions extending in the vane-longitudinal-section direction along the inner walls 71a of the body 71 that are close to the leading edge LE and the trailing edge TE, and have concave grooves 72a at the centers in cross sections of the sealing dams 72, along the vane-longitudinal-section direction.
On the other hand, at the leading edge LE side and the trailing edge TE side on the outer surface of the insert 81 (surface opposed to the inner wall 71a of the body 71), at least two flange parts 83 extending in the vane-longitudinal-section direction and in the vane-transverse-section direction are provided; and the flange parts 83 are inserted into the concave grooves 72a of the sealing dams 72. The flange parts 83 and the sealing dams 72 are brought into contact in the concave grooves 72a, so as to separate the pressure-surface-side cavity space CP having a high pressure from the suction-surface-side cavity space CS having a low pressure, thus sealing the pressure difference between both spaces.
Referring to FIG. 7, a description will be given below of the flow of cooling air blowing out from the insert 81 to the cavity spaces through the impingement holes 84 and discharged into combustion gas through the film holes 73 provided in the airfoil part 61.
Combustion gas flowing along the outer wall 71b of the turbine vane 60 has a high pressure at the pressure surface PS side and has a low pressure at the suction surface SS side. Cooling air for cooling the body 71 is supplied to the insert 81 at a higher pressure than the pressures of the combustion gas. The cooling air blows out to the pressure-surface-side cavity space CP and the suction-surface-side cavity space CS through the impingement holes 84 provided in the insert 81, thus impingement-cooling the inner walls 71a of the body 71.
Further, the cooling air blowing out from the insert 81 to the pressure-surface-side cavity space CP is discharged into combustion gas through the film holes 73 provided at the pressure surface PS side of the body 71 of the airfoil part 61. The cooling air blowing out to the suction-surface-side cavity space CS is discharged into combustion gas through the film holes 73 provided at the suction surface SS side of the airfoil part 61. Due to the pressure difference between combustion gas flowing in the pressure surface PS side of the body 71 and that flowing in the suction surface SS side thereof, the pressure in the pressure-surface-side cavity space CP becomes higher than the pressure in the suction-surface-side cavity space CS.
However, in the conventional example shown in FIG. 7, one insert 81 is disposed in each of the cooling chambers C1, C2, and C3, and cooling air supplied to the insert 81 is supplied to the pressure-surface-side cavity space CP and the suction-surface-side cavity space CS through the impingement holes 84, is used to cool the inner walls 71a of the body 71, and is then used to film-cool the outer surface of the airfoil part 61. However, when only one insert 81 is provided in each cooling chamber, it is difficult to carry out appropriate film cooling.
Specifically, in the above-described configuration, since the pressure surface PS side of the body 71, which is located at the upstream side of combustion gas, has a higher temperature than the suction surface SS side of the body 71, which is located at the downstream side of the combustion gas, it is necessary to enhance impingement-cooling for the pressure surface PS of the body 71 more than that for the suction surface SS of the body 71.
On the other hand, since the pressure-surface-side cavity space CP has a higher pressure than the suction-surface-side cavity space CS, the pressure difference with respect to the insert 81 is low in the pressure-surface-side cavity space CP and is high in the suction-surface-side cavity space CS. Therefore, in order to sufficiently apply impingement-cooling to the inner wall 71a of the body 71 at the pressure surface PS, it is necessary to increase the number of the impingement holes 84 that communicate with the pressure-surface-side cavity space CP and to reduce the number of the impingement holes 84 that communicate with the suction-surface-side cavity space CS.
Without such hole-count adjustment, impingement-cooling for the suction surface SS of the body is enhanced, compared with that for the pressure surface PS of the body, and the amount of cooling air for the suction surface SS is increased. In other words, the amount of air used for impingement-cooling the suction surface SS becomes excessive with respect to the pressure surface PS, the suction surface SS of the body is excessively cooled, and the amount of cooling air for the entire blade is increased, thus reducing the cooling efficiency of the gas turbine.
However, when the number of impingement holes on the suction surface SS of the body is reduced more than the number of impingement holes on the pressure surface PS of the body, the pitch of impingement holes is increased at the suction surface SS of the body, thus causing a temperature variation in the body and increasing the thermal stress on the body.
Further, as described above, since the pressure in the pressure-surface-side cavity space CP is higher than the pressure in the suction-surface-side cavity space CS, the pressure difference with respect to the insert 81 is low in the pressure-surface-side cavity space CP and is relatively high in the suction-surface-side cavity space CS. Therefore, as shown in dashed lines 82 in FIG. 7, the suction surface SS of the insert 81 expands outward in a vane transverse cross section, causing a problem of deformation of the whole insert.
Further, when the insert is deformed, the seal gap between the flange parts 83 of the insert and the concave grooves 72a of the sealing dams 72 deteriorate, and, as indicated by the direction of arrows in FIG. 7, cooling air leaks from the pressure-surface-side cavity space CP toward the suction-surface-side cavity space CS, causing a problem of deterioration of the seal gap between the suction side cavity and the pressure side cavity.
In order to suppress the deformation of the insert, a method of improving the strength of the insert by providing ribs or dimples on the insert or a method of improving the strength of the insert by increasing the plate thickness of the insert can be used. However, these methods of improving the strength of the insert cause a problem in manufacturability of the inserts.
In addition to the cooling chamber C1, which is closest to the leading edge LE, shown in FIG. 7, the adjacent cooling chamber CS2 also has the above-described problems.